Electrical systems and machinery may be operated using alternating current (AC) power or direct current (DC) power. Power controllers can be used to connect and disconnect electrical loads to AC or DC input power. Power controllers often make use of a switch, such as a relay or a solid state switch connected between the source of input power and the load. A processor controls the operation of the switch to connect the load to input power when the load is to be operated and to disconnect the load under certain conditions. For example, the power controller may disconnect a load when the input power is at levels that could damage the load.